Solution

Open /etc/nagios/nrpe.cfg on the remote Nagios NRPE server...

vi /etc/nagios/nrpe.cfg

... and add the IP address of your Nagios/Icinga host (1.2.3.4 in this example) to the allowed_hosts line:

[...]
# ALLOWED HOST ADDRESSES
# This is an optional comma-delimited list of IP address or hostnames
# that are allowed to talk to the NRPE daemon.
#
# Note: The daemon only does rudimentary checking of the client's IP
# address. I would highly recommend adding entries in your /etc/hosts.allow
# file to allow only the specified host to connect to the port
# you are running this daemon on.
#
# NOTE: This option is ignored if NRPE is running under either inetd or xinetd
allowed_hosts=127.0.0.1,1.2.3.4
[...]

Save the file and restart the NRPE server:

/etc/init.d/nagios-nrpe-server restart

About Falko Timme

Falko Timme is an experienced Linux administrator and founder of Timme Hosting, a leading nginx business hosting company in Germany. He is one of the most active authors on HowtoForge since 2005 and one of the core developers of ISPConfig since 2000. He has also contributed to the O'Reilly book "Linux System Administration".